Electronic devices typically include modules such as different subsystems, circuits and so on. For example, tablet computers, smart phones, music players etc. may include therein power amplifiers, monitors and so on. Respective modules of an electronic apparatus typically require different supply voltages for achieving normal operations thereof. For example, an analog power amplifier may require a supply voltage of 3.5 volt, a digital processing module may require different supply voltages of 1.8 volts, 5 volts etc. Moreover, when an electronic apparatus is in different operation modes, the supply voltages required by the respective modules may also vary.
An electronic apparatus is often equipped with a power supply with a specific voltage, for example, in a battery-powered electronic apparatus, the battery may probably only supply a voltage of 3.9 volts to 4.5 volts. To ensure the normal operations of the respective modules in the electronic apparatus, a voltage converter is required to convert a direct current (DC) voltage level (e.g., a voltage from the battery) into another different DC voltage as required by an individual module, that is, a specific input voltage Vin is converted into a different output voltage Vout.
In the conventional voltage converters, for example, electric energy at an input port is transitorily stored in an inductor and/or a capacitor (i.e., a charging process is performed), and thereafter electric energy is released at a different voltage at an output port (i.e., a discharging process is performed), so that the input voltage Vin is converted into the desired output voltage Vout. Accordingly, driving signals are employed to drive a control component (e.g., a switch), by which the charging process and the discharging process are controlled so as to obtain the desired output voltage Vout, that is, a turn-on time Ton during which a corresponding switch is turned on to charge and a turn-off time Toff during which the switch is turned-off to discharge are controlled. The turn-on time Ton corresponds to a pulse width of the driving signals.
In some voltage converters, a situation where the input voltage Vin is very close to the output voltage Vout may occur. In this situation, the turn-on time Ton needs to be shortened so as to ensure the stable output voltage Vout, especially when a load driven by the output voltage Vout is relatively light. However, as limited for example by the reaction time or the like characteristics of an electronic element, a minimum Ton_min of the turn-on time Ton can only be a finite value. In this case, the voltage converters charge and then discharge with the minimum turn-on time at a part of a work cycle, and halt the charging and discharging at the other part of the work cycle, in order to provide a balanced average power, which causes the output voltage to be unstable and causes big ripples to appear. A single charging process and a single discharging process are implemented in each work cycle, and as the work cycle of the voltage converter gets shorter and shorter, that is, the switching frequency becomes higher and higher, the aforesaid problem becomes particularly prominent.